The injection of powdered, reagent such as magnesium powder, calcium silicide or calcium carbide powder into a pool of molten metal is effected by inserting a hollow elongated lance into the pool of metal and by forcing powdered reagent conveyed by carrier gas downwardly through the lance and into the metal pool in order to perform certain processes such as desulphurization of iron or steel or add alloying ingredients for example. The high temperature of the molten metal contrasted with the relatively low ambient temperature above the surface of the pool of metal imposes a severe stress on the lance and may effect a rupture thereof usually at the slag line at the surface of the pool of molten metal. Should this condition occur, flow of powdered reagent is diverted to the surface of the pool of metal rather than downwardly below the surface where it may become intermingled with the metal in a proper manner. Should the powdered reagent escape through a rupture in the lance at the surface of the pool of molten metal, the reagent is generally wasted and may constitute a dangerous fire hazard particularly if the reagent is in the form of magnesium powder or calcium carbide powder. It has been the practice to minimize the danger and waste of such a condition through the agency of an alert operator who manually shuts off the flow of reagent when the lance becomes ruptured. Of course this type of control is dependent upon the human element which is highly variable from individual to individual and of course is quite expensive.
Another cause for failure of a lance may be due to the fact that it becomes clogged by the reagent due to an insufficient rate of flow of the carrier gas or possibly due to the fact that the reagent may melt and then become solidified to a degree as it proceeds downwardly through the lance from its entry end to its exhaust end. This condition results in a choking or substantial reduction in the flow of carrier gas. In this instance it has been the practice to monitor the instruments indicating the rate of flow by means of an alert operator who when the condition develops simply shuts off the flow of reagent.
In either of the above instances in addition to shutting off the flow of reagent powder, the operator ordinarily promptly initiates elevation of the lance out of the pool of molten metal and also immediately shuts off the flow of carrier gas.